An individual microelectronic component or die is usually formed from a larger substrate, typically a semiconductor wafer. Wafers most commonly are formed primarily from silicon, although other materials such as gallium arsenide and indium phosphide are also sometimes used. Semiconductor wafers have a plurality of dies arranged in rows and columns. Typically, the wafer is sawed or “diced” into discrete dies by cutting the wafer along mutually perpendicular sets of parallel lines or “streets” lying between the rows and columns.
In a typical dicing operation, a semiconductor wafer is attached to a carrier, such as by use of an adhesive, and the carrier is mounted on a table of wafer saw. The wafer saw includes a rotating dicing blade which is attached to a rotating spindle. The dicing blade has a peripheral cutting edge which may be coated with diamond particles or other abrasives to assist in cutting the semiconductor wafer. As the blade of the wafer saw is rotated, it cuts at least partially through the thickness of the wafer and is carefully guided along the streets between adjacent dies. The blade may be guided along these streets by moving the blade relative to the wafer, by moving the table of and the wafer relative to the blade, or by moving both the table and the blade.
If a blade is not precisely mounted on the spindle, the peripheral edge of the rotating blade can trace an irregular path with respect to the axis of rotation of the spindle. Commonly, a blade will be mounted with a flat blade surface clamped flush against a flat surface of a mounting hub carried by the spindle. If the blade is not properly clamped against the hub, any play in the attachment of the blade to the spindle may cause the peripheral cutting edge of the blade to oscillate or waver irregularly. Sometimes a foreign particle can become wedged between the mounting hub and the face of the blade or the mounting hub or the blade may have a burr on its surface. Such a foreign particle or burr can cause the blade to be mounted at an angle. As the shaft is rotated, the path scribed by the peripheral cutting edge of the blade will wobble.
Wavering of the blade as the shaft is rotated can cause the blade to deviate outside the intended street on the wafer, damaging dies on one or both sides of the street. Semiconductor wafers also tend to be somewhat brittle. A wavering blade can cause chipping of the surface of the wafer, damaging dies adjacent to the street even if the blade stays within the proscribed width of the street.
The difficulties associated with properly mounting dicing blades is increasing as the semiconductor industry moves toward dual-blade wafer saws. There are two varieties of dual-blade wafer saws on the market today—dual spindle saws (with parallel, side-by-side spindles) and twin spindle saws (with opposed, axially aligned spindles). One such twin spindle wafer saw is shown in FIG. 3 of U.S. Pat. No. 6,006,739, the entirety of which is incorporated herein by reference. Typically, such twin spindle dual-blade wafer saws simultaneously cut the surface of the semiconductor wafer along parallel lines using a pair of parallel dicing blades. The two blades typically have the same diameter and are rotated about a common rotation axis so they will cut the wafer to the same depth. With commercially available dual-blade wafer saws, the operator's access to the area where the blades are mounted is somewhat limited. It is often difficult for the operator to view the blades edge-on and the operator frequently must mount blades looking along or parallel to the axis of rotation. This makes it difficult for the operator to see the mounting hubs to which the blades are being attached, leading to errors in mounting the blades. In addition, it is difficult to visually confirm that both blades are properly mounted. A highly-skilled, experienced operator can sometimes observe unacceptable wobbling of a cutting blade by watching the blade as it rotates. This visual observation is made more difficult if the operator is only able to watch a face of the blade instead of the edge of the blade. In dual-blade saws, an operator's view of the front blade is largely limited to watching the face of the rotating blade and view of the rear blade is usually greatly hindered, if not completely blocked, by superimposition of the front blade between the operator and the rear blade.